This patent application claims priority based on a Japanese patent applications Nos. 2000-37771 filed on Feb. 16, 2000, 2000-247034 filed on Aug. 16, 2000 and 2000-275176 filed on Sep. 11, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image capturing apparatus and a distance measuring method for obtaining information regarding a depth-direction distance of a subject. More particularly, the present invention relates to an image capturing apparatus and a distance measuring method for obtaining the information regarding the depth-direction distance of the subject by capturing outgoing light beams from the subject that is illuminated with light.
2. Description of the Related Art
As a method for obtaining information regarding a distance to an object or information regarding a position of the object, a three-dimensional image measuring method is known in which light having a pattern of, for example, a slit or a stripe, is cast onto the object and the pattern cast onto the object is captured and analyzed. There are a slit-light projection method (light cutting method) and a coded-pattern light projection method as typical measuring methods, which are described in detail in xe2x80x9cThree-dimensional image measurementxe2x80x9d by Seiji Inokuchi and Kosuke Sato (Shokodo Co., Ltd.).
Japanese Patent Application Laid-open No. 61-155909 (published on Jul. 15, 1886) and Japanese Patent Application Laid-open No. 63-233312 (published on Sep. 29, 1988) disclose a distance measuring apparatus and a distance measuring method in which light beams are cast onto a subject from different light-source positions and the distance to the subject is measured based on the intensity ratio of the reflected light beams from the subject.
Japanese Patent Application Laid-open No. 62-46207 (published on Feb. 28, 1887) discloses a distance detecting apparatus that casts two light beams having different phases onto the subject and measures the distance to the subject based on the phase difference between the light beams reflected from the subject.
Moreover, xe2x80x9cDevelopment of Axi-Vision Cameraxe2x80x9d, Kawakita et al., 3D Image conference ""99, 1999, discloses a method for measuring the distance to the subject in which the subject that is illuminated with light having the intensity modulated at a very high speed is captured by a camera having a high-speed shutter function, and the distance to the subject is measured from the degree of the intensity modulation that varies depending on the distance to the subject.
The conventional measuring method using light projection measures the distance to a region of the subject onto which the projection pattern is projected based on the principle of trigonometrical measurement. Thus, in order to obtain a high resolution in the distance measurement, it is necessary to arrange a projection optical system at a position sufficiently distant from a capturing optical system in principle, thus increasing the size of the measuring apparatus inevitably. Moreover, since an optical axis of the projection optical system is apart from that of the capturing optical system, there is a shadow region in which the projected pattern cannot be viewed because of the shadow of the subject when the region is viewed from the capturing optical system, thereby generating a xe2x80x9cblind regionxe2x80x9d from which distance information cannot be obtained.
In the distance measuring apparatus and the distance measuring method disclosed in Japanese Patent Applications Laid-open Nos. 61-155909 and 63-233312, the time difference occurs in the measurement because it is necessary to successively cast the light from the different emission positions to measure the reflected light beams. Thus, in a case of the moving subject, the distance cannot be measured. In addition, during a time period in which the position of the light source is changed to change the emission position, the measurement difference may occur because of waver of the capturing apparatus.
Moreover, in a case of using light beams having different wavelength characteristics, the light beams can be emitted simultaneously and the reflected light beams can be separated by a filter selected in accordance with the wavelength characteristics of the light beams so that the intensities of the reflected light beams can be measured. However, if the reflectivity of the object varies depending on the wavelength, the intensities of the reflected light beams are also different depending on the wavelength thereof. The difference of the reflected-light intensities between the wavelengths may cause an error when the depth-direction distance is calculated from the ratio of the intensities of the reflected light beams, thereby preventing the precise calculation of the depth-direction distance.
The distance measuring apparatus disclosed in Japanese Patent Application Laid-open No. 62-46207 requires a high-precision phase detector for detecting the phase difference. This makes the apparatus expensive and loses the simplicity of the apparatus. In addition, since this apparatus measures the phase of the reflected light beam from a point of the subject, it cannot measure the depth distribution of the whole subject.
Moreover, in the distance measuring method using the intensity modulation disclosed in xe2x80x9cDevelopment Axi-Vision Cameraxe2x80x9d by Kawakita et al. (3D Image Conference ""99, 1999), it is necessary to perform the light modulation and the optical shutter operation at very high speed. This causes the measuring apparatus to become large and expensive and prevents the simple measurement.
Therefore, it is an object of the present invention to provide a image capturing apparatus and distance measuring method which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, an image capturing apparatus for obtaining information regarding a depth of a subject, comprises: an illumination unit operable to cast a first illumination light beam mainly having a first wavelength and a second illumination light beam mainly having a second wavelength and a third wavelength from optically different emission positions onto the subject, the second and third wavelengths being different from the first wavelength; and a depth calculator operable to calculate a depth-direction distance to the subject based on outgoing light beams from the subject.
The illumination unit may cast the first and second illumination light beams onto the subject simultaneously. Moreover, the image capturing apparatus may further comprises: an optically converging unit operable to converge the outgoing light beams from the subject onto which the first and second illumination light beams are cast; a separation unit operable to optically separate the outgoing light beams from the subject into a first outgoing light beam having the first wavelength, a second outgoing light beam having the second wavelength and a third outgoing light beam having the third wavelength; a light-receiving unit operable to receive the first, second and third outgoing light beams that are separated by the separation unit and are converged by the optically converging unit; and a light intensity detector operable to detect intensities of the first, second and third outgoing light beams received by the light-receiving unit, wherein the depth calculator calculates the depth-direction distance to the subject by using the intensities of the first, second and third outgoing light beams.
The light-receiving unit may include three panels of solid state image sensors, while the separation unit separates the first, second and third outgoing light beams by using an optical path splitter so as to allow the first, second and third outgoing light beams to be received by the three panels of solid state image sensors, respectively. Alternatively, the light-receiving unit may include a solid state image sensor, and the separation unit may include a first optical filter that transmits light having the first wavelength, a second optical filter that transmits light having the second wavelength and a third optical filter that transmits light having the third wavelength, the first, second and third optical filter being arranged alternately on a light-receiving surface of the solid state image sensor.
The illumination unit may include a first optical filter that transmits light having a shorter wavelength than a first boundary wavelength and a second optical filter that transmits light having a longer wavelength than a second boundary wavelength. In this case, the illumination unit casts the first and second illumination light respectively transmitted by the first and second optical filters from the optically different emission positions onto the subject; the separation unit includes first, second and third optical filters that transmits light beams having the first, second and third wavelengths, respectively, the first wavelength being shorter than a shorter one of the first and second boundary wavelengths, the second and third wavelengths being longer than a longer one of the first and second boundary wavelengths; and the separation unit separates the first outgoing light beam having the first wavelength by making the outgoing light beams from the subject pass through the first optical filter of the separation unit, and separates the second light beam having the second wavelength and the third outgoing light beam having the third wavelength by making the outgoing light beams from the subject pass through the second and third optical filters of the separation unit.
The depth calculator may calculate the depth-direction distance to the subject by using a value based on the intensities of the second and third outgoing light beams and the intensity of the first outgoing light beam. The depth calculator may obtain a dummy intensity of a dummy outgoing light beam from the subject in a case where it is assumed that a light beam having the first wavelength is cast from the emission position of the second illumination light beam, based on the intensities of the second and third outgoing light beams. The depth calculator may calculate the depth-direction distance to the subject by using an averaged intensity of the second and third outgoing light beams and the intensity of the first outgoing light beam.
According to the second aspect of the present invention, an image capturing apparatus for obtaining information regarding a depth of a subject, comprises: an illumination unit operable to cast a first illumination light beam mainly having a first wavelength and a second illumination light beam mainly having second and third wavelengths that are different from the first wavelength from optically different emission positions onto the subject; and a depth calculator operable to calculate a depth-direction distance to the subject based on outgoing light beams from the subject.
The illumination unit may cast the first illumination light and the second illumination light beam simultaneously. The illumination unit may cast the first illumination light mainly having the first wavelength and the second illumination light mainly having the second and third wavelengths from the optically different emission positions onto the subject, the second wavelength being shorter than the first wavelength, the third wavelength being longer than the first wavelength. In this case, the image capturing apparatus may further comprises: an optically converging unit operable to converge outgoing light beams from the subject onto which the first and second illumination light beams are cast; a separation unit operable to optically separate the outgoing light beams from the subject into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a light-receiving unit operable to receive the first and second outgoing light beams converged by the optically converging unit; and a light intensity detector operable to detect intensities of the first and second outgoing light beams received by the light-receiving unit, wherein the depth calculator calculates the depth-direction distance to the subject by using the intensities of the first and second outgoing light beams.
The light-receiving unit may include two panels of solid state image sensors, while the separation unit optically separates an optical path of the first outgoing light beam from that of the second outgoing light beam by using an optical path splitter to allow the first and second outgoing light beams to be received by the two panels of solid state image sensors, respectively. Alternatively, the light-receiving unit may include a solid state image sensor, and the separation unit includes a first optical filter that transmits light having the first wavelength and a second optical filter that transmits light having the second and third wavelengths, the first and second optical filters being arranged alternately on a light-receiving surface of the solid state image sensor.
The depth calculator may calculate the depth-direction distance to the subject based on a ratio of the intensity of the first outgoing light beam and a half of the intensity of the second outgoing light beam.
In the image capturing apparatus according to any of the first and second aspects of the present invention, an optical axis of the illumination unit when the illumination unit casts the first and second illumination light beams may be substantially coincident with an optical axis of the capturing unit when the capturing unit captures the outgoing light beams from the subject. The light intensity detector may detect the intensities of the first and second outgoing light beams in each pixel of an image of the subject captured by the light-receiving unit, and the depth calculator calculates a depth distribution of the subject by obtaining for each pixel the depth to a region of the subject corresponding to the pixel.
In the image capturing apparatus according to any of the first and second aspects of the present invention, the first and second illumination light beam may be light beams in an infrared region, the separation unit may further include a device operable to optically separate visible light from the outgoing light beams from the subject, and the light-receiving unit may further include a solid state image sensor for visible light operable to receive the visible light that is optically separated by the separation unit and is converged by the optically converging unit.
In the image capturing apparatus according to any of the first and second aspects of the present invention, the image capturing apparatus may further comprise a controller operable to control at least one of emission periods, the intensities, and the emission positions of the first and second illumination light beams cast from the illumination unit and an exposure period of the light-receiving unit, based on at least one of the intensities of the outgoing light beams from the subject detected by the light intensity detector and the depth-direction distance to the subject calculated by the depth calculator.
According to the third aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step of casting a first illumination light beam mainly having a first wavelength and a second illumination light beam mainly having second and third wavelengths from optically different emission positions onto the subject simultaneously, the second and third wavelengths being different from the first wavelength; a separation step of separating outgoing light beams obtained from the subject that is illuminated with the first and second illumination light beams into a first outgoing light beam having the first wavelength, a second outgoing light beam having the second wavelength and a third outgoing light beam having the third wavelength; a capturing step of capturing the first, second and third outgoing light beam that are separated; a light intensity detection step of detecting intensities of the first, second and third outgoing light beams that are captured; and a depth calculation step of calculating a depth-direction distance to the subject by using the intensities of the first, second and third outgoing light beams.
In the depth calculation step, the depth-direction distance to the subject may be calculated by using a value based on the intensities of the second and third outgoing light beams and the intensity of the first outgoing light beam. In the depth calculation step, a dummy intensity of a dummy outgoing light beam from the subject in a case where it is assumed that a light beam having the first wavelength is emitted from the emission position of the second illumination light beam may be obtained based on the intensities of the second and third outgoing light beams, and the depth-direction distance to the subject is calculated based on a ratio of the intensity of the first outgoing light beam and the dummy intensity. The depth-direction distance to the subject may be calculated based on a ratio of an averaged intensity of the second and third outgoing light beams and the intensity of the first outgoing light beam.
According to the fourth aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step of casting a first illumination light beam mainly having a first wavelength and a second illumination light beam mainly having a second wavelength and a third wavelength from optically different emission positions onto the subject, the second wavelength being shorter than the first wavelength, the third wavelength being longer than the first wavelength; a separation step of optically separating outgoing light beams from the subject onto which the first and second illumination light beams are cast into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a capturing step of capturing the first and second outgoing light beams separated from each other; a light intensity detection step of detecting intensities of the first and second outgoing light beams; depth calculation step of calculating a depth-direction distance to the subject by using the intensities of the first and second outgoing light beams.
In the depth calculation step, the depth-direction distance may be calculated based on a ratio of the intensity of the first outgoing light beam and a half of the intensity of the second outgoing light beam.
This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings.